The present invention relates generally to disc drives, and more particularly, but not by way of limitation, to an improved latch assembly for restraining the motion of an actuator in a disc drive.
Disc drives of the type where data is recorded on the surfaces of a plurality of discs are well known in the industry. Data is recorded in circular, concentric tracks on the discs, and an actuator assembly is used to move read/write heads to the chosen track for read/write operations. A typical rotary voice coil actuator consists of a pivot shaft fixedly attached to the base of the disc drive housing with the actuator housing rotatably mounted to the pivot shaft by bearings. One side of the actuator housing is a yoke supporting a coil in the magnetic field of a permanent magnet. The other side of the actuator extends into a plurality of actuator arms ending in the read/write heads. The actuator housing rotates when controlled current is provided to the coil, thereby positioning the read/write heads to the desired track. When power to the disc drive is lost or when the disc drive is not in operation, some means of restraining the rotation of the actuator arms is necessary so as to avoid damage to the disc surfaces or to the read/write heads. One known way is to move the read/write heads to a parking zone and to latch the actuator in that position until power is restored to the disc drive.
One conventional latching system involves a first latch member that is fixed relative to the base of the disc drive housing and a second latch member that is attached to the yoke of the actuator. The second latch member is thus capable of travelling in a substantially horizontal arcuate path about the pivot shaft. The first latch member is generally vertical and located near the permanent magnet of the voice coil magnet assembly so that it is capable of holding the second latch member by magnetic attraction when the disc drive is not in operation. The first member also forms part of the voice coil motor (VCM) magnet assembly in that it is fixed between an upper plate and a lower plate of the VCM. The permanent magnet is usually bonded to the lower plate which in turn is mounted to the base of the disc drive housing. The coil of the VCM moves within a gap between the permanent magnet and the upper plate.
The conventional way of assembling the first latch member involves first mounting the lower plate to the base of the disc drive housing. The lower plate includes a hole extending generally downward, into which a rod-like lower end of the first latch member is loosely inserted from the top. The actuator assembly has to be next mounted to the base of the disc drive housing before the upper plate is fitted on. A hole or a recess in the lower surface of the upper plate serves to locate the upper end of the first latch member. It is only when the upper plate is attached that the first latch member is secured in place. Before that assembly step, the first latch member tends to drop out of the rectangular hole either because it is attracted by the permanent magnet or because of the vibrations suffered in its travel to subsequent assembly stations.
Attempts to overcome this problem includes providing a threaded lower end for the first latch member so that it can be directly screwed into the lower plate or to the base of the disc drive housing, as shown in FIG. 8 of the U.S. Pat. No. 6,115,222 issued to Andrews et al. on Sep. 5, 2000.
As designers look for cheaper and faster alternatives to using screw attachments, the use of interference fit has been explored. This involves having small lateral protrusions at the lower end of the first latch member so that there is an interference fit with a hole in the lower plate of the VCM as the first latch member is driven downwards into the hole. Although this has the advantage of enabling the VCM supplier to provide the disc drive manufacturer with a lower plate that is pre-assembled with the first latch member, special tooling will be needed to fit the first latch member into the hole in the lower plate. In addition, it is suspected that such a fitting introduces particles into the disc drive environment, and may be detrimental to disc drive performance.
There is therefore a need for an improved first latch member and VCM assembly that can be assembled with greater ease and at lower cost.
The present invention relates to a disc drive component that is part of a magnetic latch as well as part of a voice coil motor (VCM) magnet assembly.
The present invention provides for an assembly for use in a disc drive. According to a most preferred embodiment, the assembly includes a lower plate which defines an elongate slot. The lower plate has a magnet fixed on one surface of the base. The assembly also includes a first latch member that has a stem which is meant for engagement with the elongate slot. The stem ends off at one end in a step which is brought into abutment with another surface of the base when the first latch member is attracted by the magnet. According to one embodiment of the present invention, the elongate slot has an opening at a side of the lower plate for receiving the stem into the elongate slot. According to another embodiment, the elongate slot does not lead to an opening in the side of the lower plate, but may used in conjunction with a first latch member that has a step with an elongate cross-section. The elongate slot may further include at least one bend for locating the stem in abutment with an end of the elongate slot nearer the magnet.
The present invention avoids the need for screw attachment or force fitting. In addition, the assembly of an upper plate with the lower plate is not necessary to prevent the first latch member from dropping out of engagement with the lower plate. That is, the first latch member can be pre-assembled with the lower plate by the VCM supplier before it is assembled with the rest of the disc drive components by the disc drive manufacturer. These and various other features as well as advantages which characterize the present invention will be apparent upon reading of the following detailed description and review of the associated drawings.